#!/bin/sh
i=2
j=1
while [[ $j -le 10 ]]
do
   echo '2 **' $j = $i 
   i=`expr $i '*' 2` 
   j=`expr $j + 1` 
done

echo ${j:-work}
echo ${k:-notexisted}

echo ${j:=word}
echo ${k:=word}

echo ${j:+"j existed"}  # used to check var whether existed
echo ${k:+word}
